Oxidative dehydrogenation of alkenes or alkadienes to furan compounds

ABSTRACT

Alkenes and/or alkadienes are contacted with molecular oxygen and an oxidative dehydrogenation catalyst consisting essentially of phosphorus, iron, and oxygen, with the iron-to-phosphorus atom ratio being in the range of about 2:1 to about 20:1.

nited States Patent Farina, Jr. et al.

[ Dec. 23, 1975 OXIDATIVE DEHYDROGENATION OF ALKENES OR ALKADIENES TOFURAN COMPOUNDS Inventors: Floyd E. Farha, Jr.; Marvin M.

Johnson; Donald C. Tabler, all of Bartlesville, Okla.

Assignee: Phillips Petroleum Company, Bartlesville, Okla.

Filed: Aug. 16, 1973 Appl. No.: 389,738

US. Cl 260/346.l R; 252/435; 252/437; 260/680 E; 260/604 R int. Cl. C07D307/36 Field of Search 260/2461 R, 680 E References Cited UNITED STATESPATENTS 3,716,545 2/1973 Ripley 260/346.l R

Primary Examiner-Henry R. Jiles Assistant Examiner-Bemard l. Dentz [57]ABSTRACT 13 Claims, No Drawings OXIDATIVE DEHYDROGENATION OF ALKENES ORALKADIENES TO FURAN COMPOUNDS This invention relates to oxidativedehydrogenation catalysts and the use thereof for the conversion ofalkenes and/or alkadienes to furan Compounds.

Furan compounds can react readily with oxygen under oxidation conditionsto produce ring cleavage and the formation of polymers. Accordingly, theproduction of furan compounds by the oxidative dehydrogenation ofhydrocarbons has generally been avoided.-

Recently it has been discovered that furan compounds can be produced bythe oxidative dehydrogenation of hydrocarbons in the presence of certainspecific catalysts without substantial conversion of the furan compoundsto undesirable products. The search for additional catalysts suitablefor this reaction continues.

Accordingly, it is an object of the present invention to provide a newand improved oxidative dehydrogenation catalyst. Another object of theinvention is to provide a new and improved process for the conversion ofalkenes or alkadienes to furan compounds. Other objects, aspects andadvantages of the invention will be apparent from a study of thespecification and the appended claims to the invention.

In accordance with the present invention there is provided an improvedcatalyst for the production of furan type compounds from alkenes andalkadienes having from 4 to carbon atoms, which catalyst consistsessentially of phosphorus, iron, and oxygen wherein theiron-to-phosphorus atom ratio is in the range of about 2:1 to aboutpreferably in the range of about 2.511 to about 10:1, and morepreferably in the range of about 3:1 to about 6:1.

If desired, these catalysts can be supported on conventional solidcatalytic support materials, for example zinc oxide, silica, alumina,boria, magnesia, titania, zirconia, and mixtures thereof. Where acatalyst support is employed, the support will generally constitute fromabout 10 to about 98, preferably from about 75 to about 95, weightpercent of the total catalyst composition. Supports having a surfacearea in the range of about 2 to about 50 m /g, and preferably in therange of about 5 to about 20 m /g, are desirable.

The catalysts of the present invention can be prepared by many suitabletechniques, for example coprecipitation, impregnation, ion exchange,aqueous or nonaqueous solution or suspension mixing, or dry mixing. Ingeneral, any method can be employed which will provide a compositioncontaining the desired elements in the defined proportions, and whichhas a catalytic surface area in the range of about 0.05 to about 20 m/g, preferably in the range of about 0.1 to about 5 m g. Thus thecatalyst components and/or compounds thereof can be combined in anysuitable manner. Any compound of iron or phosphorus can be employed inthe preparation of the catalyst so long as none of the compounds aredetrimental to the final oxidative dehydrogenation catalyst andessentially all of the elements in the compounds employed, other thanthe iron, phosphorus, and oxygen, are removed from the final catalyst bywashing or by volatilization. However, small or trace amounts of someother elements which can be involved in the preparation of the catalystcan be tolerated in the final catalyst composition. For example, if

alkali metal or alkaline earth metal hydroxides are employed in thepreparation of the catalyst, very small residual amounts of such alkalimetal and alkaline earth 2 metals are not detrimental. Similarly if ironsulfate is employed in the preparation of the catalyst, small residualamounts of sulfur can be tolerated.

Generally, however, the preferred iron compounds are the oxides orphosphates of iron or compounds which are converted to the oxide orphosphate on calcination. Thus, suitable iron compounds include theoxides, phosphates, nitrates, halides, sulfates, oxalates, acetates,carbonates, propionates, tartrates, hydroxides, and the like. Examplesof these compounds include iron hydroxide, iron propionate, iron oxide,iron nitrate, iron acetate, iron phosphate, iron chloride, ironcarbonate, and the like, and admixtures thereof. The presently preferredphosphorus compounds include the phosphorus oxides, the ammoniumphosphates, iron phosphate, and the various forms of phosphoric acid,and the like, and admixtures thereof. Examples of suitable phosphoruscompounds are iron phosphate, phosphoric acid, phosphorus pentoxide,diammonium hydrogen phosphate, and the like, and admixtures thereof. Theterm phosphate includes not only the monophosphate ion, P0 but alsopolyphosphate is an integer in the range of 2 through 100.

One technique for forming an unsupported catalyst of the presentinvention comprises mixing one or more phosphorus compounds, and one ormore iron compounds.

The compounds can be admixed in the form of dry compounds and thencalcined. They can be admixed in the presence of a diluent to form apaste and/or one of the components can be employed in liquid form, suchas phosphoric acid, to form the paste. If desired the paste can be driedbefore calcining. A particle forming step such as pelletizing orscreening can precede the drying step or the calcining step.

A technique for forming a supported catalyst of the present inventioncomprises sequentially impregnating the support with solutions ordispersions of each component compound, drying and calcining theimpregnated support.

The calcining step will be accomplished under conditions which ensurethe conversion of any nonoxide or nonphosphate compounds to the oxide orphosphate form and the volatilizing of any undesired elements. Ingeneral the calcining step comprises heating the catalyst composition toa temperature in the range of about 800 F to about 1500 F for a time inthe range of about 1 to about 40 hours. Presently preferred calciningconditions comprise a temperature in the range of about 850 F to about1400 F for a time in the range of about 2 to about 24 hours in thepresence of a molecular oxygen-containing gas, for example, air.

Suitable feeds for conversion to furan compounds include the unsaturatedacyclic hydrocarbons, particularly the acyclic alkenes and acyclicalkadienes having from 4 to 10 carbon atoms. Examples include nbutene-l,butene-2, n-pentene-l, isopentene, hexenel, heptene-2, octene-l decenel, Z-methyIbutene-l, hexene-3, 2-ethylbutene-l, 2-methylpentene-3, 3-ethylhexene-2, butadiene-l,3, pentadiene-l,3, isoprene, hexadiene-l ,3,decadiene-l,3, and the like, and mixtures thereof. The acyclicalkadienes having from 4 to 5 carbon atoms are presently preferred.

The furan compounds produced by the process of the present inventionhave the formula wherein each R is individually selected from the groupconsisting of hydrogen and alkyl radicals having from 1 to 6 carbonatoms, the total carbon atoms in the R radicals being in the range of to6. Representative products include furan, 2-methy1furan, 3-methylfuran,2,5-diethylfuran, 2-n-hexy1furan, 2-isopropyl-3*methy1- furan,3,4-di(n-propyl)furan, 3-methy1-4-n-buty1furan and the like.

In accordance with the present invention a hydrocarbon feed comprisingone or more acyclic alkenes and /or one or more acyclic alkadienes iscontacted, under suitable reaction conditions for conversion to furancompounds, with a molecular oxygen containing gas in the presence of thehereinabove defined catalyst. The molecular oxygen containing gas can behigh purity oxygen, oxygen diluted with an inert diluent such asnitrogen, flue gas containing residual oxygen, air, and any source ofmolecular oxygen which is at least essentially free of contaminantswhich would be detrimental to the desired reaction. In a presentlypreferred embodiment, the oxidative dehydrogenation process is carriedout in the absence of any halogen. In general, the temperature will bein the range of about 500 F. to about l200 F., and preferably will be inthe range of about 700 F. to about 1 100 F. Any suitable pressure can beemployed, but in general the pressure will be in the range of about 0.05to about 250 psig, and preferably will be in the range of about 0.1 toabout 25 psig. The hydrocarbon feed rate will generally be in the rangeof about to about 1000 standard cubic feet of alkenes and/or alkadienesper hour per cubic foot of catalyst bed (GHSV), and preferably will bein the range of about 100 to about 500 GHSV. The mol ratio of molecularoxygen to alkenes and alkadienes will generally be in the range of,about 0.121 to about 3:1, and preferably will be in the range of about0.5:1 to about 2:1. Steam can be employed in the reaction zone as adiluent and heat transfer agent. When steam is utilized, the mol ratioof steam to alkenes and alkadienes will generally be in the range ofabout 0.1:1 to

4 about 1, and preferably will be in the range of about 5:1 to about30:1.

The alkenes, if present, are largely converted to the correspondingalkadienes. The alkadienes, in turn, are converted in significantquantities to the corresponding furan compounds. However, the reactioneffluent can also contain unreacted feed material, alkenes includingethylene, propylene and butenes, water, oxides of carbon,alkenylcycloolefin, 4-viny1cyc1ohexene, crotonaldehyde, acetaldehyde andother oxygenated products. The furan compounds can be recovered bysuitable techniques, for example by condensation from the reactor gaseffluent followed by distillation. Unconverted alkenes and/or alkadienescan be recovered and recycled to the reactor, as can other materialssuch as crotonaldehyde which are convertible to furan compounds underthe reaction conditions. If desired, the conversion of alkenes to furancompounds can be conducted in two reaction zones in series. The firstreaction zone can be operated under conditions favorable for theconversion of the alkenes to alkadienes, while the second reaction zonecan be operated under conditions favorable to the conversion of thealkadienes to furan compounds. The effluent from the first reaction zonecan be subjected to conventional separation techniques to recoverunconverted alkenes for recycle to the first reaction zone and aconcentrated alkadiene stream for feed to the second reaction zone. Ifdesired, the total effluent from the first reaction zone can be passeddirectly to the second reaction zone without separation. The effluent ofthe second reaction zone can be processed for recovery and recycle ofunreacted alkadienes to the second reaction zone and for recovery of afuran compound product. The catalyst of the present invention can beemployed in both reaction zones, or another suitable dehydrogenationcatalyst can be employed in the first reaction zone while the presentcatalyst is utilized in the second reaction zone.

The following example is presented in further illustration of theinvention and should not be construed in undue limitation thereof.

EXAMPLE In a series of runs, 400 GHSV butadiene, 400 GHSV oxygen and8000 GHSV steam were contacted in the presence of about 2 cubiccentimeters of the respective catalyst. Other reaction conditions andresults are set forth in the following table:

TABLE Conversion Selectivity Selectivity of Furan to Acetaldehyde toFuran and Atom Ratio Butadiene Yield Furan Yield Acetaldehyde Run Iron/PTemperature 'F Mole mole Runs for the catalysts of runs 1. toweregenerally made with eachcatalystat700 E, 800F, 900F, and 1000F, and,only 1 those; runs producing "significant quantities of furan areshown. ,The' runs for the catalysts of runs 17 to 22were made-onlyatthe. indicated ,tem perature. The catalysts of runs 1 2, 4 10 werepregive the atom ratios shown in the Table. The quantity of catalystprepared was about grams o'r'less. Each mixture was calcined at 850F for7 hours, then at 1000F for l 1 hours. The catalysts of runs 3 and 1 1-15were prepared by mixing together sufficient Fe O and NH H PO to give theatom ratios shown in the Table. The catalyst of run 16 was made bypouring sufficient H PO over Fe O to give the atom ratio shown in theTable. After soaking, without stirring, the mixture was calcined at1000F for 17 hours. This mixture was prepared to give an inhomogeneouscatalyst.

The catalysts of runs 17-22 were prepared by mixing together sufi'rcientl e- 0 and H PO to give the atom ratios shown in the Table. Each mixturewas calcined at 1000F for 18 hours. About 20 gram lots of catalyst wereprepared. Each mixture was calcined at 1200F for 24 hours.

The gaseous effluents, on a dry basis, were analyzed by means ofgas-liquid chromatography. Products found included unreacted butadiene,furan, acetaldehyde, carbon oxides, ethylene, propylene and butenes. Thereported selectivities to furan and furan plus acetaldehyde are modifiedselectivities based on the above gaseous product analyses. The yields offuran and acetaldehyde are in terms of mols per 100 mols of butadienefeedstock.

Runs 1-3 are made with prior art catalysts, rich in phosphorus. Theresults show that a catalyst with a Fe/ P ratio of 0.94/ 1 is efiectivein producing substantial amounts of furan from a relatively modestconversion (16.3%) of butadiene. The catalyst of run 1 was nonuniform inappearance with mixed red and white portions. It is believed the activeportions of the catalyst reside in the interfaces between the red andwhite portions and hence the true iron/phosphorus ratio is unknown. Thecatalyst of run 16 was made in an effort to ih'ithetange of 2:1 to about20:1 under suitable vaporphase reaction conditions for; the conversionof said at least one unsaturated acyclic .feed hydrocarbon to at v leastoiie fu ran compound having the formula pared by mixingtogethensufficient Fe O and l-l PO to g wherein each R is individuallyselected from the group consisting of hydrogen and alkyl radicals havingfrom 1 to 6 carbon atoms, the total carbon atoms in the R radicals beingin the range of 0 to 6; and recovering at least a portion of the furancompounds thus produced.

2. A process in accordance with claim 1 wherein said feed hydrocarboncomprises at least one acyclic alkadiene having from 4 to 5 carbonatoms.

3. A process in accordance with claim 2 wherein said ratio is in therange of about 2.511 to about 10:1.

4. A process in accordance with claim 3 wherein said reaction conditionscomprise a temperature in the range of about 500F to about 1200F, anunsaturated acyclic hydrocarbon feed rate in the range of about 10 toabout 1000 GHSV, and a mol ratio of oxygen to unsaturated acyclic feedhydrocarbon in the range of about 0.121 to about 3:1.

5. A process in accordance with claim 4 wherein said feed hydrocarboncomprises butadiene.

6. A process in accordance with claim 5 wherein said iron-to-phosphorusatom ratio is in the range of about 3:1 to about 6:1.

7. A process which comprises reacting at least one unsaturated acyclicfeed hydrocarbon selected from the group consisting of alkenes andalkadienes having from 4 to 10 carbon atoms, with oxygen in contact witha catalyst consisting essentially of iron, phosphorus and oxygen, withthe iron-to-phosphorus atom ratio being in the range of 2:1 to about20:1, under suitable reaction conditions for the conversion of said atleast one unsaturated acyclic feed hydrocarbon to at least one obtain asimilar non-homogeneous catalyst composifuran compound having the f ltion. The results showed the latter catalyst to be inactive at theconditions used. Thus the catalyst of run 1 may be a fluke. However, theresults also indicate that a catalyst even slightly richer in phosphorusis much less effective in converting butadiene (4.8 and 2.5% in separateruns) to furan (1.4% and 0.1%). The catalysts of the invention arephosphorus-poor. That is, the iron/phosphorus ratio is at least 2/1rather than being less than 1/1 as in prior art catalysts. Inspection ofthe data indicate that significant quantities of furan are produced whenthe Fe/P ratio ranges from about 3/1 to about 6/1. The data show aminimum amount of furan is produced at a Fe/P ratio of about 1.45/1 tosome value approaching 0.94/1. Thus, an

unexpected criticality in operable ranges of phosl. A process whichcomprises reacting at least one unsaturated acyclic feed hydrocarbonselected from the group consisting of alkenes and alkadienes hav ng from4 to 10 carbon atoms, with oxygen in contact with wherein each R isindividually selected from the group consistig of hydrogen and alkylradicals having from 1 to 6 carbon atoms, the total carbon atoms in theR radicals being in the range of O to 6; said reaction conditionscomprising a temperature in the range of about 500F to about 1200F, anda pressure in the range of about 0.05 to about 250 psig; and recoveringat least a portion of the furan compounds thus produced.

8. A process in accordance with claim 7 wherein said feed hydrocarboncomprises at least one acyclic alkadiene having from 4 to 5 carbonatoms.

9. A process in accordance with claim 8 wherein said ratio is in therange of about 2.521 to about 10:1.

10. A process in accordance with claim 9 wherein said temperature is inthe range of about 700F to about 1 F and said pressure is in the rangeof about 0.1 to about 25 psig.

7 8 11. A process in accordance with claim 10 wherein 12. A process inaccordance with claim 11 wherein said reaction conditions furthercomprise an unsatusaid feed hydrocarbon comprises butadiene. ratedacyclic hydrocarbon feed rate in the range of 13. A process inaccordance with claim 7 wherein about 10 to about 1000 GHSV, and a mo]ratio of 5 said iron-to-phosphorus atom ratio is in the range of oxygento unsaturated acyclic feed hydrocarbon in the about 3:1 to about 6: 1.range of about 0.1:] to about 3:l.

1. A PROCESS WHICH COMPRISES REACTING AT LEAST ONE UNSATURATED ACYCLICFEED HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF ALKENES ANDALKADIENES HAVING FROM 4 TO 10 CARBON ATOMS, WITH OXYGEN IN CONTACT WITHA CATALYST CONSISTING ESSENTIALLY OF IRON, PHOSPHORUS AND OXYGEN. WITHTHE IRON-TO-PHOSPHORUS ATOM RATIO BEING IN THE RANGE OF 2:1 TO ABOUT20:1 UNDER SUITABLE VAPORPHASE REACTION CONDITIONS FOR THE COVERSION OFSAID AT LEAST ONE UNSATURATED ACYCLIC FEED HYDROCARBON TO AT LEAST ONEFURAN COMPOUND HAVING THE FORMULA
 2. A process in accordance with claim1 wherein said feed hydrocarbon comprises at least one acyclic alkadienehaving from 4 to 5 carbon atoms.
 3. A process in accordance with claim 2wherein said ratio is in the range of about 2.5:1 to about 10:1.
 4. Aprocess in accordance with claim 3 wherein said reaction conditionscomprise a temperature in the range of about 500*F to about 1200*F, anunsaturated acyclic hydrocarbon feed rate in the range of about 10 toabout 1000 GHSV, and a mol ratio of oxygen to unsaturated acyclic feedhydrocarbon in the range of about 0.1:1 to about 3:1.
 5. A process inaccordance with claim 4 wherein said feed hydrocarbon comprisesbutadiene.
 6. A process in accordance with claim 5 wherein saidiron-to-phosphorus atom ratio is in the range of about 3:1 to about 6:1.7. A process which comprises reacting at least one unsaturated acyclicfeed hydrocarbon selected from the group consisting of alkenes andalkadienes havinG from 4 to 10 carbon atoms, with oxygen in contact witha catalyst consisting essentially of iron, phosphorus and oxygen, withthe iron-to-phosphorus atom ratio being in the range of 2:1 to about20:1, under suitable reaction conditions for the conversion of said atleast one unsaturated acyclic feed hydrocarbon to at least one furancompound having the formula
 8. A process in accordance with claim 7wherein said feed hydrocarbon comprises at least one acyclic alkadienehaving from 4 to 5 carbon atoms.
 9. A process in accordance with claim 8wherein said ratio is in the range of about 2.5:1 to about 10:1.
 10. Aprocess in accordance with claim 9 wherein said temperature is in therange of about 700*F to about 1100*F and said pressure is in the rangeof about 0.1 to about 25 psig.
 11. A process in accordance with claim 10wherein said reaction conditions further comprise an unsaturated acyclichydrocarbon feed rate in the range of about 10 to about 1000 GHSV, and amol ratio of oxygen to unsaturated acyclic feed hydrocarbon in the rangeof about 0.1:1 to about 3:1.
 12. A process in accordance with claim 11wherein said feed hydrocarbon comprises butadiene.
 13. A process inaccordance with claim 7 wherein said iron-to-phosphorus atom ratio is inthe range of about 3:1 to about 6:1.